In recent years, there is known a back irradiation complementary metal-oxide semiconductor (CMOS) image sensor having a layered structure in which a circuit board on which a drive circuit is formed is prepared in addition to a sensor board on which a photoelectric converter is formed and the circuit board is bonded to a surface opposite to a light receiving surface of the sensor board.
In such a CMOS image sensor, the layered structure is formed by connecting a surface of a wiring layer of the sensor board and a surface of a wiring layer of the circuit board. Furthermore, a connecting part for electrically connecting the sensor board and the circuit board is provided. In the connecting part, a through via hole that penetrates a semiconductor layer of the sensor board and is connected to the wiring layer of the sensor board and another through via hole that penetrates the sensor board and is connected to the wiring layer of the circuit board are connected to each other by a wiring part formed on an upper part of the light receiving surface of the semiconductor layer of the sensor board. Furthermore, a color filter and an on-chip lens corresponding to each pixel are provided on the light receiving surface side of the semiconductor layer of the sensor board.
Here, the shorter a distance between the color filter and the photoelectric converter becomes, the better sensitivity and a color mixing characteristic becomes. Furthermore, a thickness of the semiconductor layer on the light receiving surface side (length in a direction perpendicular to the sensor board) is preferably small in order to relax restriction of a circuit wiring and an alignment mark, stress of the sensor board, and the like. Accordingly, a thickness of a region around the wiring part is made thinner than the wiring part, and the wiring part forms a step on the light receiving surface side of the semiconductor layer. As a result, in a case where the color filter is applied after the formation of the wiring part, coating unevenness of the color filter is caused due to the step.
Furthermore, with respect to a solid-state imaging device such as a front irradiation CMOS image sensor and a charge coupled device (CCD) image sensor as well, in a case where a wiring part is formed around a region on a semiconductor substrate where a pixel is formed in such a manner that a thickness of the wiring part is larger than that of the region, coating unevenness of the color filter is caused due to the step of the wiring part.
In view of the above, a technique in which a corner portion to be an end region of a step structure is made to have a curvature shape has been proposed (see Patent Document 1) as a method for suppressing resist application unevenness (above-described coating unevenness) caused by the step structure disposed around an imaging region of the back irradiation CMOS image sensor.
Moreover, in the technique disclosed in the Patent Document 1, the shape of the corner portion is not limited to the curvature shape, and it is also proposed to make, by adding an obtuse angle corner, the corner portion to have an obtuse shape or a shape of a combination of a rounded and obtuse angles.
Moreover, a technique in which an application unevenness is reduced by disposing a through chip via (TCV) in only one direction in a longitudinal or lateral direction and reducing an area of a step region has been proposed (see Patent Document 2).